<!DOCTYPE html>
<body>
<style>
body {
    display: flex;
    height: 200px;
}

#container1 {
    position: relative;
}

#container2 {
    position: absolute;
    height: 100%;
    display: flex;
}

#container3 {
    display: flex;
}
</style>
<div id="container1">
<div id="container2">
<div id="container3">
<input type="text" placeholder="Username">
</div>
</div>
</div>
</body>
